John Calvin Commentary 2 Thessalonians 1:8

"rendering vengeance to them that know not God, and to them that obey not the gospel of our Lord Jesus:" — 2 Thessalonians 1:8 (ASV)

Who will inflict vengeance. To better persuade believers that the persecutions they endure will not go unpunished, he teaches that this also involves the interests of God Himself, since the same persons who persecute the godly are guilty of rebellion against God. Therefore, it is necessary for God to inflict vengeance upon them not merely for our salvation, but also for His own glory.

Furthermore, this expression, who will inflict vengeance, relates to Christ, for Paul indicates that this office is assigned to Him by God the Father. However, it may be asked whether it is lawful for us to desire vengeance, for Paul promises it, as if it could be lawfully desired. I answer that it is not lawful to desire vengeance upon anyone, since we are commanded to wish well to all.

Besides, although we may, in a general way, desire vengeance upon the wicked, yet, since we do not yet distinguish them, we should desire the welfare of all. Meanwhile, the ruin of the wicked may lawfully be looked forward to with desire, provided a pure and properly regulated zeal for God reigns in our hearts, and there is no feeling of inordinate desire.

Who know not. He distinguishes unbelievers by these two marks: that they know not God, and obey not the gospel of Christ. For if obedience is not given to the gospel through faith, as he teaches in the first and last chapters of the Epistle to the Romans (Romans 1:18 and following, Romans 16:17–19), unbelief is the cause of resistance to it.

He charges them at the same time with ignorance of God, for a living knowledge of God itself produces reverence towards Him. Therefore, unbelief is always blind, not as if unbelievers were entirely lacking in light and intelligence, but because they have their understanding darkened so that seeing they do not see (Matthew 13:13).

It is not without good reason that Christ declares that this is life eternal, to know the true God, etc. (John 17:3). Accordingly, from the lack of this salutary knowledge, contempt of God follows, and finally, death. On this point I have discussed more fully in commenting on the first chapter of First Corinthians.